There has been a physical quantity measuring device including a measuring unit for measuring a physical quantity, such as the flow rate, the pressure, the temperature, or the humidity of ages to be measured. For example, the measuring unit for measuring a physical quantity includes a flow measuring device including a flow measuring element. The flow measuring element includes a thermal, flow measuring element, and the thermal, flow measuring element is a sensor having a heater element and a thermopile element formed on a silicon substrate, and measuring the flow rate in a measuring unit based on transfer of heat of the heater element.
The flow sensor can measure a wide flow range, has a relatively good accuracy, and is inexpensive, so that the flow sensor is widely used for consumer measuring instruments and industrial measuring instruments. Further, in recent years, integration density of large-scale integrated circuits has been considerably increasing and size-to-performance efficiency thereof has been extremely increased, and now the large-scale integrated circuits are used for every consumer/industrial electronic device.
In an automotive field, for example, an intake air flow measuring device is used for an internal-combustion engine, and the intake air flow measuring device at least includes a casing forming an auxiliary air passage, and a flow sensor disposed in the auxiliary air passage (sub-passage). The intake air flow measuring device is disposed in a main passage (also referred to as an intake pipe), and intake air flowing in the main passage is partially taken into the auxiliary air passage. A flow rate detection unit of the flow sensor outputs a signal according to a flow rate of the intake air taken into the auxiliary air passage, the flow sensor has a large-scale integrated circuit (signal processing unit), and the large-scale integrated circuit processes the output signal.
In particular, in recent years, an electronically-controlled fuel injection device has been generally used for automobiles, but in an engine compartment, sensors or control devices are closely disposed. Consequently, the number of harnesses for connecting various sensors and control devices for controlling the sensors is increased, and the harnesses are complicated. Thus, the sensors or control devices have been integrated with each other to reduce the number of parts and further improve internal appearance of the engine compartment.
Therefore, in terms of reduction in number of parts and improvement in appearance, a unit for measuring a physical quantity other than the intake air flow rate, such as a temperature measuring unit, a humidity measuring unit, or a pressure measuring unit has been integrated into a device.
For example, as an example of such a device, PTL 1 discloses “a mass intake air flow measurement device integrally incorporating a mass air flow measurement device for measuring a mass intake air flow in an air intake tube and a humidity sensing device for sensing humidity in the air intake tube, the mass intake air flow measurement device including a mass air flow sensing element for sensing the mass intake air flow, the mass air flow sensing element being mounted in a bypass passage into which part of air flowing in the air intake tube is drawn, and a humidity sensing device for sensing humidity, the humidity sensing device being mounted in a second bypass passage opened in the bypass passage”.